I finally found a couple of exhaust manifolds for my 74 L-48. they have the correct casting number (3932461) and are not drilled for air tubes.The only other casting number is either RH 8, or RH 6. Can you tell me what that means? Is that the date 1968 ? Do I need to find RH 4 for 1974? What should I put on them after I get them steel shot, any suggestions? As always, thanks for the help, Corky.
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Re: exhaust manifold date
I believe that the RH6 (or 4 or 8) identifies the mold that was used to cast the manifold. That way, if something was wrong, Chevrolet could go to that particular mold and correct the problem.
Anyway, the casting date is on the back side on the manifold (closest to the engine). It is almost impossible to see when the manifold is installed, which is why it is not normally judged. The casting date only specifies the month and day (i.e. E15 for May 15th). No year is indicated.
I had the original manifolds for my 73 bead blasted, and they came out great. My manifolds did not have any pitting, just a lot of surface rust. I highly recommend having them bead blasted. After that, perhaps a coat of calex (spelling?) manifold dressing. -
Re: exhaust manifold date
I agree wholeheartedly with Ed on this. Lots of folks see alpha numeric codes and leap to the conclusion that they're some kind of date code. Some are some aren't. All the coding info was there to backtrack to the source in case troubles were observed. If you think GM had a single mold for high volume parts, think again! We see this all the time on stuff like water outlets, tranny cases, Etc....Comment
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